General SCARA (4x4 Coupled) Robot Module

This robot module controls a SCARA mechanism with four or five degrees of freedom. The linear axis (Z) may be either joint 2 or joint 3.

Module Specifications

Minimum V+ compatibility:  13.0

V+ License Requirements:  “Kinematics License”

If you install this module but do not have the above license, an “*Option not installed*” message will be displayed when you restart your system.

Device module name:  SCC

Device module identification number: 24

This number is displayed with the robot serial and model number after the system boots up, and whenever the ID monitor command is issued.

Default startup message: "General SCARA (4x4 Coupled) Robot Module"

The startup message is displayed just after the system boots up.

Default joint configuration (for V+ 13.0 and higher):

Joint	Axis	Board/Channel
1	1 ("shoulder")	1/1
2	2 ("elbow" or Z)	1/2
3	3 (Z or "elbow")	1/3
4	4 (Roll)	1/4
5	5 (Pitch)	2/1

With multiple robots, it will be necessary to correct the joint configuration from the SPEC program to avoid conflicts.

Robot Option Word

Bit 4: Linear axis selection: joint 2 / joint 3

The robot option word determines whether the SCARA robot's linear axis (Z) is joint 2 or joint 3.  If bit 4 (counting from 1; option word value 8) is set, then the linear axis is joint 2; if not, it is joint 3.  See the AdeptMotion VME Developer's Guide for details on setting the robot option word.

Axis Configuration

1. Joint 1 is a revolute axis that rotates about the world Z axis. A positive change in joint angle corresponds to a positive rotation about the world Z axis.  When joint 1 is positioned at zero degrees, the inner link (the link between joint 1 and joint 2) will point along the world X axis.  When joint 1 is positioned at 90 degrees, the inner link will point along the world Y axis.

2. Joint 2 (joint 3 if the robot option word bit 3 is set) is a revolute axis whose axis of rotation is parallel to the first joint.  A positive change in joint angle corresponds to a positive rotation about an axis parallel to the world Z axis.  When joints 1 and 2 are positioned at zero, both the inner and the outer links will point along the world X axis.  If joint 2 is subsequently rotated to 90 degrees, the outer link will point in the positive world Y direction.

3. Joint 3 (joint 2 if robot option word bit 3 is set) is a linear axis that moves in the world Z direction.  A positive displacement of the joint moves the robot's tool in a negative (positive if robot option word bit 3 is set) world Z direction.  For a four-axis SCARA, when this joint is set to its zero position, the height of the tool mounting flange above the world X-Y plane is defined by a parameter described below.  For a five-axis SCARA, when this joint is set to its zero position, the height of the center of rotation of the fifth axis above the world X-Y plane must be specified. 

4. Joint 4 is a revolute axis that rotates the tool mounting flange (or the fifth axis) about a world Z direction.  A positive change in its joint angle corresponds to a negative rotation about an axis that is parallel to the world Z axis.  For a four-axis SCARA, when joints 1, 2, and 4 are at their zero positions, the X axis of the tool flange is pointed in the +X world direction, the Y axis is pointed in the –Y world direction, and the Z axis is pointed in the –Z world direction.

5. The optional joint 5 is a revolute axis whose axis of rotation is parallel to the X-Y world plane.  When joints 1, 2, 4, and 5 are at their zero positions, the X axis of the tool mounting flange is pointed in the +X world direction, the Y axis is pointed in the –Y world direction, and the Z axis is pointed in the –Z world direction.  If joint 5 is subsequently rotated in a positive direction, the tool mounting flange will be rotated about an axis parallel to the negative world Y axis.

Maximum operating range of rotational joints

The SCC module has motor limit stops in addition to joint limit stops. Motor limit stops are preferred over joint limit stops when using coupled axes because joint limit stops cannot accurately represent the true range of motion for coupled motors.

This module has up to four rotary joints. Their maximum operating range is as follows:

Joint 1:            -179.9° to +179.9°
Joint 2 (or 3): -179.9° to +179.9°
Joint 4:            -359.9° to +359.9°
Joint 5:            -179.9° to +179.9°

Warning
Be sure to set the software joint/motor limits properly before attempting to move the robot in a V+ program. It is especially important for revolute axes to have correct software limits set before attempting any motion instruction. If the limits are improperly set, a revolute axis can rotate unexpectedly at high speed in order to stay in range.

Variations in Axis Configuration

This module can be configured to control the first four axes of the SCARA robot or all five axes.

The linear axis (Z) may be either joint 2 or joint 3.

Geometric Dimensional Constants

There are a number of dimensional constants that are utilized by this module.  Most of the constants are a function of three primary parameters: the length of the first link (the distance from the first to the second joint axes), the length of the second link (the distance from the second to the fourth joint axes), and the height of the tool flange above the X-Y world plane when the linear joint is at its zero position.  As a convenience, the SPEC program prompts for the Tool Z-offset distance and the other three primary parameters and automatically computes all of the other required dimensional constants.  See the table below and Figures 1 and 2 for more information.

Link Dimension Parameters for SCARA Robot
	Parameter	Units	Value
LA	Tool Z-offset distance	mm
LB	Length of first link	mm	a1
LC	Length of second link	mm	a2
LD	Height of tool flange	mm	s1 + s2  – s3

Figure 1.  Link Definitions and Dimensions for a SCARA Robot with a Linear Joint 2

Figure 2.  Link Definitions and Dimensions for a SCARA Robot with a Linear Joint 3

Interpretations of Cartesian Rotation

During program-generated straight-line motions, the first Cartesian rotation speed and acceleration parameters control the rate at which the tool mounting flange (joint 4) rotates about a vector pointed in the +Z world direction. 

For a five-axis SCARA, the second Cartesian rotation speed and acceleration parameters control the rate at which joint 5 rotates during straight-line motions.

Coupling Between Robot Joints and Motors

A full 4-by-4 matrix is used to represent the coupling between the first four motors. Therefore, every possible linear coupling relationship between any of the four motors can be represented, and compensated for, by this module.

Robot Configuration Control Program Instructions

The following robot configuration-control program instructions are utilized to specify the range of motion for the outer link:

LEFTY, RIGHTY

(See the V+ Language Reference Guide for more information on these instructions.)

The following robot configuration-control program instructions do not have any effect upon the operation of mechanisms controlled by this module:

ABOVE, BELOW, FLIP, NOFLIP

Additional Restrictions

None.